Self Injection length in La0.7 Ca0.3 Mno3-YBa 2Cu3O7-d ferromagnet- superconductor multi layer thin films

We have carried out extensive studies on the self-injection problem in barrierless heterojunctions between La0.7Ca0.3MnO3 (LCMO) and YBa2Cu3O7-d (YBCO). The heterojunctions were grown in situ by sequentially growing LCMO and YBCO films on LaAlO3 (LAO) substrate using a pulsed laser deposition (PLD) system. YBCO micro-bridges with 64 microns width were patterned both on the LAO (control) and LCMO side of the substrate. Critical current, Ic, was measured at 77K on both the control side as well as the LCMO side for different YBCO film thickness. It was observed that while the control side showed a Jc of ~2 x 10E6 A/ cm2 the LCMO side showed about half the value for the same thickness (1800 A). The difference in Jc indicates that a certain thickness of YBCO has become 'effectively' normal due to self-injection. From the measurement of Jc at two different thickness' (1800 A and 1500 A) of YBCO both on the LAO as well as the LCMO side, the value of self-injection length (at 77K) was estimated to be ~900 A self-injection length has been quantified. A control experiment carried out with LaNiO3 deposited by PLD on YBCO did not show any evidence of self-injection.Comment: 6 pages, one figure in .ps forma

Ion beam synthesis of germanium nanostructures

Si and Ge nanocrystals embedded in SiO(2) have attracted much attention due to their possible application in integrated optoelectronic devices. Ion beam mixing of Ge film into fused silica to form Ge nanoparticles is one of the possible methods to controllably produce embedded nanoclusters. In this work, Ge nanocrystals in fused silica were formed by defect induced nucleation and ion beam mixing. In our experiment, we have created defects in fused silica using 200 keV Ar ions with different fluences ranging from 1 x 10(15) to 2 x 10(16) ions/cm(2) (pre-mixing irradiation). Ce film (20 nm) was then deposited on it and ion beam mixed using 230 keV Ar ions at a fluence of 2 x 10(16) ions/cm(2). The Ge-SiO(2) composite films were characterized using UV-visible and Micro-Raman spectroscopy. UV-visible spectra showed variation in absorption band gap with ion beam fluence used for pre-mixing irradiation. Micro-Raman spectra showed formation of Ge nanoparticles in SiO(2). (C) 2009 Elsevier B.V. All rights reserved

Studies on La0.7Ca0.3MnO3-YBa2Cu3O7-delta heterostructures grown by pulsed laser deposition technique

Pulsed laser deposition (PLD) is a unique method for growing highly stoichiometric, materials in the form of epitaxial thin films. Here we discuss the optimization of deposition parameters for laser ablation of multi-component La0.7Ca0.3MnO3-YBa2Cu3O7-delta (LCMO-YBCO) heterostructures grown in situ by sequential deposition of LCMO and YBCO on (100) LaAlO3 (LAO) substrates using a PLD system. We discuss the growth of these multi-layers, from the device applications point of view

STUDY OF ALUMINUM-OXIDE FILMS FORMED BY PLASMA ANODIZATION

Anodic oxidation plays an important role in microelectronics as well as in thin film devices. Oxide films obtained on metals such as aluminium and tantalum by anodization using a gaseous electrolyte are found to be superior to those formed by using aqueous solution. Earlier researchers have shown that anodization can be carried out more efficiently at an optimum pressure of 6.7 Pa (50 mTorr) and an optimum bias voltage of 5V. It is also reported that the optimum pressure depends on the system geometry. This work was carried out to determine the effect of cylindrical geometry. It is observed that the optimum pressure for the cylindrical geometry is 26.8 Pa (200 mTorr) while the optimum bias voltage is found to be 5V. Formation of Al2O3 is confirmed by using electron spectroscopy for chemical analysis. Small-angle X-ray diffraction results indicate the formation of the gamma-Al2O3 phase at low bias voltages whereas the beta-Al2O3 phase is more dominant at higher bias voltages

Self-injection length of polarized spins in La(0.7)Ca(0.3)MnO(3)-YBa(2)Cu(3)O(7-delta) ferromagnet-superconductor heterostructures

Studies on the self-injection length of polarized spins in La(0.7)Ca(0.3)MnO(3) (LCMO)-YBa(2)Cu(3)O(7-delta) (YBCO) heterostructures on LaAlO(3) (LAO) substrates fabricated in situ with pulsed laser deposition have been carried out. The measured critical current density, J(c) of YBCO microbridges on LAO (control) arm was found to be larger than that of the microbridges on the LCMO arm. The difference in J(c) in the two arms indicates that a certain thickness of YBCO has become effectively normal due to self-injection of spin-polarized carriers. Further, by measuring transition temperature T(c) of YBCO layers with ac susceptibility, it has been found that the thickness of the non-superconducting YBCO layer, due to self-injection at the interface, depends upon the LCMO thickness. Both the above experiments led us to estimate the maximum thickness of the non-superconducting YBCO layer at the interface due to self-injection of spin polarized quasi-particles from YBCO into LCMO; this thickness is found to be in the range 650-850 Angstrom for LCMO thickness greater than or equal to 1000 Angstrom. A control experiment performed on YBCO-LNO (LaNiO(3)) heterostructure did not show any evidence of self-injection

GLANCING-ANGLE X-RAY-DIFFRACTION AND X-RAY PHOTOELECTRON-SPECTROSCOPY STUDIES OF NITROGEN-IMPLANTED TANTALUM

Polycrystalline tantalum thin foils are implanted with molecular nitrogen ions.X-ray photoelectron spectroscopy results show preferential nitrogen loss during implantation and argon sputtering

Role of rapid thermal annealing in the formation of crystalline SiGe nanoparticles

In the present work, we report the formation of SiGe nanoparticles embedded in SiO(2) film by atom beam sputtering method in conjunction with Rapid Thermal Annealing (RTA). Crystalline SiGe nanoparticles in the co-sputtered films are formed after rapid thermal annealing at 900 degrees C and 1000 degrees C for 1 min in N(2) gas ambient. These nanoparticles were characterized using UV-vis absorption, GXRD, FTIR and Raman measurements. UV-vis spectra show blue shift of absorption edge with the increase in annealing temperature. GXRD pattern shows that particles formed are crystalline. The average size of the nanoparticle estimated from GXRD is 15 nm to 30 nm for the films annealed at temperatures 800 degrees C and 1000 degrees C respectively. FTIR spectra show the phase separation between SiGe nanoparticles and SiO(2) matrix after RTA. Raman spectra show that SiGe phase is formed with c-Ge as core and c-SiGe as shell in the SiO(2) matrix. (C) 2009 Elsevier B.V. All rights reserved